The purpose of this study is to determine an optimum lung hyperinflation volume that will produce minimal changes in mean arterial pressure (MAP) and prevent post-suctioning hypoxemia. The sample will consist of 50 male post-coronary artery bypass graft patients who are at least four hours post surgery and determined to be hemodynamically stable according to set criteria. The subjects will receive three consecutive lung hyperinflations at one of the four randomly ordered volumes (12cc/Kg, 14cc/Kg, 16cc/Kg, and 18cc/Kg of lean body weight) in 15 seconds via the Ma1 ventilator "sigh" control at FI02 100% MAP will be monitored continuously. The lung hyperinflation will be immediately followed by suctioning with a 14FR catheter. Suction (200mmHg flow rate 16L/min) will be applied to the catheter continuously while rotating and withdrawing for 10 seconds. The three lung hyperinflations (at the set volume, followed by suctioning will be repeated x 3. Following the last suction pass, arterial blood gases will be withdrawn at time 0, 30, 60, 120, 180, and 300 seconds post-suctioning. The protocal will be repeated one hour later until all four folumes have tested. The results of this study will provide nurses with parameters for administering lung hyperinflation to critically ill patients.